1. Field of the Invention
The present invention relates generally to a cable assembly for use in an FTTx optical network, and more specifically, to a low-profile fiber optic cable assembly including a flexible cable access location, tether and slack coil utilizing bend performance optical fiber.
2. Description of the Related Art
Engineered fiber optic cable assemblies are being developed to deliver services to subscribers over optical networks. These networks are commonly referred to as “FTTx” networks, wherein “FTT” stands for “Fiber-to-the” and “x” is used to generically describe a location such as a premises, home, office, desk, building, etc. An engineered cable assembly typically includes at least one mid-span access location, or tap point, at a predetermined position along the cable length at which one or more pre-selected optical fibers are preterminated and routed away from the remaining uncut optical fibers of the cable, typically through at least one tether. The term “preter-minated” is used herein to refer to a fiber that is cut at a position upstream of its end. The mid-span access location and at least one tether are used for the lateral branching of optical fibers from an attached cable. The tether includes at least one optical fiber that is optically connected, typically spliced, to the preterminated fibers of the cable. The downstream end of the tether may terminate in splice-ready optical fibers, connectorized optical fibers or a tethered assembly, among others.
Engineered cable assemblies must be capable of withstanding installation forces placed upon them and must be able to be installed within a variety of installation environments, for example, within small diameter conduit. Therefore, it would be desirable to provide a cable assembly capable of being installed within conduit less than about 2 inches, more preferably less than about 1.5 inches, while resisting damage to the assembly, and particularly the fibers and splices within, during installation. Various examples of engineered cable assemblies commonly include the splice interface of the distribution cable fibers and tether fibers to be maintained within some form of closure. Rigid closures are typically inflexible to a variety of installation environments and are typically too large to be successfully installed within small diameter conduit. Flexible closures, in contrast, are typically more flexible to installation environments, but often include strength or preferential bend elements to force the flexible closure to take a predetermined shape when encountering a corner or sheave wheel. This is most often due to the use of a straight through approach of the splice fibers and the need for protecting spliced fibers routed off of the neutral axis of the cable fibers. Additional strength and bending elements are undesirable in that they require an added element, potentially form a tear point and do not always prevent a mid-span access point from flipping over, especially at high tensile loads.
A specific example of a component heavy, semi-flexible closure is described in U.S. Pat. No. 5,440,665 entitled “Fiber Optic Cable Assembly Including Main and Drop Cables and Associated Fabrication Method” (the '665 patent). The '665 patent describes a cable access point at which pre-selected optical fibers are branched, spliced and routed separately from the remaining uncut optical fibers of the distribution cable. The '665 patent states that the spliced fibers are straight through routed and must be devoid of a slack coil of optical fiber and has dimensions smaller than sufficient to accommodate the minimum bend radius of a slack coil thereof. An example of a rigid closure is described in U.S. Pat. No. 5,210,812 entitled “Optical Fiber Cable Having Spliced Fiber Branch and Method of Making Same” (the '812 patent). The '812 patent describes a rigid, clam-shell closure including pins for preventing a slack coil from forming within the closure, thus also providing a straight through approach in a larger and inflexible package. While the '665 closure is a straight through design for small diameter installation environments, it is a requirement that it be sized small enough so that it cannot accommodate a slack coil. The '812 closure also does not include a slack coil, and it is further an inflexible closure, making it difficult to install through conduit or around a sheave wheel.
Thus, what is needed is an engineered cable assembly including a mid-span access location that is substantially encapsulated with a flexible body and including an advantageous slack coil within the body, all the while providing a package capable of being installed through conduit less than about 2 inches in diameter, more preferably less than about 1.5 inches in diameter. A slack coil having a large amount of fiber in a small diameter package would be advantageous in that it may remove the need for a stiff element to make the body take a predetermined shape, and would also accommodate temperature and tensile induced fiber length changes. Further, a slack coil provided using a bend performance, bend insensitive or bend optimized fiber would allow for a slack coil without increasing the size of the package, a design not possible using conventional closures and standard single mode fiber.